Complex disease states such as metastatic cancers and acute atherosclerosis take a staggering toll on society in terms of mortality and health care costs. Current approaches to discriminate these pathologies are limited by their invasive nature, costs, and inability to target molecular features of the pathologies using real-time tracking methods. This exploratory R21 study is based on an innovative nanoscale concept to resolve and monitor tissue pathology using molecularly targeted optical imaging nanoprobes that emit infrared light. Infrared light is attractive because can be easily transmitted through thick biological tissues. Our nanoprobes consist of rare earth doped ceramic nanoparticles, which brightly emit infrared light in a novel window of emission. These particles are encapsulated with albumin nanoshells to impart cytocompatibility and aqueous dispersion and the albumin is conjugated with markers to target the disease of interest. The project proposes to develop a repertoire of rare earth-doped nanoparticles encapsulated in functionalized albumin nanoshells to establish nanoprobes with high biological availability in vivo, improved biocompatibility, and functional targeting to disease targets. A particularly innovative endpoint proposed is that of tracking disease phenotype progression through the in vivo imaging of intravenously injected cocktail of nanoprobes emitting across different infrared wavelengths and functionalized to four different markers of disease phenotypes. Two specific aims are proposed. In Aim 1, the project will investigate the role of nanoscale size and biofunctionalization of the rare earth nanoprobes on the biodistribution and accumulation at disease sites using a murine metastatic melanoma model. The in vivo distribution will be examined using infrared imaging of living animals and compared against conventional tissue profiles using high resolution inductively coupled mass spectrometry. Thus, optimal formulations of nanoprobes for in vivo imaging will be established. In Aim 2, the nanoprobe rare earth doped nanoparticles will be tailored to emit at different wavelengths and thus create a family of multi-chromatic nanoparticles. These will be functionalized to report simultaneously on four key markers for growth, invasiveness, and metastatic potential of tumors . The relative accumulation of the multiplexed nanoprobes will be used to track the progression/stabilization of tumors following established drug treatment. This will serve as a proof of concept for the foundations of this R21 project, and be the basis for developing this nanotechnology for a broader range of disease states of varying molecular phenotypes.